The **FRS-R-4** is a specific model of industrial-grade cartridge fuse belonging to the **Fusetron™** family, manufactured by **Bussmann (Eaton)**. It is a heavy-duty, dual-element, time-delay fuse designed for motor and inductive load protection. --- ## Technical Specifications | Feature | Specification | | :--- | :--- | | **Model Number** | FRS-R-4 | | **Amperage Rating** | 4 Amps | | **Voltage Rating (AC)** | 600 Vac | | **Voltage Rating (DC)** | 300 Vdc | | **Interrupting Rating** | 200,000A (RMS Symmetrical) | | **Fuse Class** | Class RK5 | | **Type** | Dual-Element, Time-Delay | | **Physical Size** | 5.0" Length x 0.81" Diameter | --- ## Key Electronic Characteristics ### 1. Dual-Element Design The FRS-R-4 contains two distinct components working in series: * **Thermal Cutout:** Handles low-level overloads. It provides a "time-delay" which allows temporary surges (like motor startups) to pass without blowing the fuse. * **Short-Circuit Element:** A high-speed notched ribbon that reacts instantly to heavy short-circuit currents to protect downstream components from catastrophic failure. ### 2. Time-Delay Functionality Standard fuses blow instantly when current exceeds the rating. The FRS-R-4 allows for a specific duration of overcurrent (typically 10 seconds at 500% of the rated current). This prevents "nuisance tripping" caused by the inrush current of electric motors. ### 3. Current Limitation Despite being a time-delay fuse, the FRS-R-4 is **current-limiting**. In the event of a massive short circuit, it clears the fault so fast that it prevents the peak current from ever reaching its full potential, significantly reducing electromagnetic stress on the circuit. ### 4. Rejection Feature (The "-R" Suffix) The "R" in the model name signifies a **Rejection** feature. The fuse has a specific physical notch in the end cap. This ensures that it can only be installed in Class R fuse holders, preventing someone from accidentally replacing it with a lower-rated, non-current-limiting fuse. --- ## Typical Applications * **Motor Branch Circuits:** Its primary use is protecting small motors (around 1-2 HP depending on voltage) where startup current is high. * **Transformers:** Protecting the primary side of control power transformers. * **Solenoids:** Handling the inductive kicks of electromagnetic coils. * **General Feeder Protection:** Where high interrupting capacity (up to 200kA) is required for safety. ---